Signaling apparatus



March 27, 1928. 1,663,880

J. c. GABRIEL ET AL S I GNALI NG APPARATUS Filed A112. 3, 1925 4y My Patented M". '27, 1928.

UNITED STATES PATENT; OFFICE."

JOHN c. GABRIEL AND ononen M. nruRsroN; on NEW 1031:, N. 1., AssIeNons r WESTERN ELECTRIC COMPANY, INCORPORATED, or NEW YORK, N. A coarona TION OF NEW YORK.

SIGNALING ArrABA'rUs.

Application filed August a, 1925. Serial Ho. 47,055.

5 cessive detection. is used to recelve an 1ncoming wave comprising an unmodulated com onent and both side bands, one cause of distortion is that which results from the interaction of two incoming waves WlllCll happen to differ from each other by a fre-. quency interval corresponding to the 1ntermediate frequency to be used in the receiving system. 1

In this case the beat current produced by the interaction of the two waves will be transmitted through the intermediate frequency selective and amplifying circuits and will interact with the signal modulated intermediate frequencywave resulting from the incoming wave to be received, to produce an interfering tone in the indicator or receiving instrument.

When the incoming wave comprises a S] gnal modulated carrier wave consistlng of a carrier component and both side-band components, the received signal is frequently distorted due to the two side bands beating together or combining to produce a current of audible frequency that may combine with the modulating current to produce an lnterfering tone in the indicator or telephone receiver.

Again, difiiculty is frequently experienced in radio reception, especially at short wave lengths due to the periodic increase and decrease in the volume of the received signal, commonly called fading. One reason for this may be a phase shift between the two side bands of the signal modulated wave in the transmission medium, which causes irregular operation of the receiver.

One object of this invention is to prevent interference, in a system of the above mentioned type, due to undesired beats produced by combining two incoming waves.

Another object is to prevent distortion of the signals caused by the side bands of a modulated wave being combined.

These objects and others, which will be a arent as the nature of the invention is disclosed, are accomplished by providing a receiving system inwhich a single side band of a transmitted signal modulated carrier wave is selected. In a receiving systememvided between the intermediate frequency amplifier and the last detector, which is ca pable of passing without appreciable attenuation only a single side band of the intermediate frequency wave. Local oscillations of intermediate carrier frequency are supplied to the last detector. Beat currents produced by the interaction of two incidentally received signal waves which differ from each other by a frequency adapted to be freely transmitted through the interme .diate frequency selective means are eliminated by employing a push-pull detector in the first stage of detection. Beatcurrents caused by combining the unmodulated intermediate frequency component, which is not suppressed by the selective circuit or filter, and the side band transmitted through the filter, are eliminated by employing a second detector of the push-pull type.

Although the novel features which are believed to be characteristic of this invention will be pointed out with particularity in the claims appended hereto, the invention itself, as to its object and advantages,the mode of its operation and the manner of its organization will be better understood by referring to the following description taken in is impressed upon the push-pull detector 1 of a receiving system employing successive detection. The receiving circuit is shown, by way of illustration, as a loop aerial 2 tuned by condenser, 3. Waves from a local oscillator 4 are impressed upon the gridfilament circuit of the push-pull detector 1 through transformer 5 having its secondary winding connected to the common input connection in the filament lead of the detector. When oscillations are supplied in this manner, variations in the tuning of the loop circuit will not alter the impedance of the oscillation circuit. This is especially advantageous with loop receivers, as when the local oscillator is once set, its frequency will not ibe changed by tunin the loop. detector of this type is disc osed in U. S. Patent 1,343,308, June 15, 1920 to Carson, to which reference may be made for a description of its method of operation. Although a particular type of oscillator has been shown, any other suitable source of oscillations may be employed to produce oscillations having a frequency differing from the frequency of the ncoming signal Wave by an amount adapted to combme with the received wave to produce a wave of desired intermediate frequency.

The intermediate frequency wave is impressed upon the amplifier 6, herein shown as comprising four stages of amplification. However, since the purpose of the amplifier 6 is merely to increase the amplitude of the intermediate frequency wave so that a signal of the desired intensity is produced in the indicator, it may consist of any number of stages.

Amplifier 6 consists of space discharge devices 7 coupled by transformers 8 which are designed to cooperate with the devices 7 to selectively amplify a wave of predetermined intermediate frequency. Polarizing potential is applied to the grids or control electrodes of the amplifier tubes'7 by the sources 9. Condensers 10 serve to by-pass high frequency current around the various direct current sources.

The intermediate frequency wave after being amplified by the amplifier 6 is supplied to a filter 11 or 12', either of which. may be included in the circuit by actuating the switch 13. Filter '11 is designed to pass without appreciable attenuation both side bands and the unmodulated component of the intermediate frequency wave, while filter 12 is designed to freely pass only one side band and to suppress the second side band and the unmodulated carrier component of intermediate frequency.

Waves passed through filter 11 or 12 are impressed upon the second detector 14 through transformer 15 and detected. The current resulting from this stage of detection may he amplified by an audio frequency amplifier 16,- if desired, and used to actuate phone receiver 17.

As shown, the local oscillations produced 'anv suitable indicating means, such as a teleby an oscillator 19 are-amplified by a device 20, and impressed upon-the resistance 18 included in the grid filament circuit of detector 14. The device 20 serves to amplify the oscillation produced by source 19 to the desired intensity and toprevent variations in load impedance from affecting the frequency of the oscillations generated. Obviously, if

the source 19 supplies oscillations of desired intensity the amplifier 20 would not be used.

Source 21 supplies space current to the various space discharge devices. Filament heating current supplied from source 22.

When the switch 13 is in a position to connect filter 11 into the circuit the filament heating circuit for one of the push-pull detectors 14 is open at contact 23, and the filament heating current of tubes 19 and 20. is open at contact 24. N

In the operation of this system with switch 13 thrown to the right to connect filter 12 in the circuit, waves received by the antenna circuit 2 are combined with oscillations from the local-source 4 to produce a signal modulated wave-of intermediate frequency which is amplified by intermediate frequency amplifier 6.

Two incidentally received high frequency waves having a frequency difference equal to the above, intermediate frequency will be impressed symmetrically upon the input circuit of the push-pull detector 1 and consequently they will not be combined therein to produce a beat note. There will there-' fore be no extraneous wave tending to produce an interfering tone,

Although filter 12 is designed to pass only a single side band and to suppress the second side band and the unmodulated carrier component, there may pass through this filter some small portion of the unmodulated component which would combine with the transmitted side band to produce an interfering tone in the receiver 17 However, by using a push-pull detector 14, which operates in a manner similar to push-pull detector 1, the unsuppressed unmodulated component and the transmitted side band will be symmetritransmitted through the intermediate frequency circuits.

cally impressed upon the input circuit of de- I tector 14, so that this component will not be combined with the side band to produce a beat current.

When it is desired to employ both side bands of the intermediate frequency wave, switch 13 is thrown to the left to connect filter 11 into the circuit and to interrupt the filament heating circuit of one of the two ill] detectors 14, oscillator 19 and amplifier 20,

whereby one of the tubes 14, the local source 19 and the amplifier 20 are rendered inoperative. If both detector tubes 14 were euergized, the modulation products and the umnodulated carrier component of the inproved by connecting filter 12 the circuit and selecting only a'single side band. 'Ihe use-of reviously known systems employing successive detection has been unsatisfactory in certain localities where a large number of transmitting stations are located due to the signals from two stations combining to produce a beat current which interferes with the wave in the intermediate frequency amlifier. The beat note may be due to waves incoming from two undesired stations, or a wave from an undesired station and the desired signaling wave being combined in the first detector. In such localities the 0b]LC tionable interference is eliminated by use of a receiving apparatus-employing a push-pull detector as shown in the above described system.

, Although this invention has been shown and described as embodied in a particular system operating in a-particular manner, it is not to be limited thereto, but only in accordance with the scope of the invention as defined by the following claims.

What is claimed is:

1. In a signaling system, means for receivin an incoming wave carrying signals, a local oscillator, means for combining said received wave with oscillations supplied by said local oscillator to produce an intermediate frequency wave carrying signals, means for suppressing a portion of said 1ntermediate frequency wave, means for 10- cally supplying energy of the frequencv of at least a part of said suppressed portion of the intermediatefrequency wave, and means for combining said local energy with the unsuppressed portion of said intermediate frequency wave to produce signal currents.

'2. A system of the character described com rising means for receiving a wave 1ncludlng modulated and unmodulated components, a source of local oscillations, means for combining said local oscillations with said received wave to produce an intermediate frequency signal modulated wave, means for suppressing the unmodulated component thereof, a local oscillator for supplying locally oscillations of the frequency o the unmodulated component, means for combining said locally supplied oscillations with the modulated components of said intermediate frequency wave to produce a low frequency signal, and means for indicating said low frequency signal.

3. In a signaling system, means for receiving a wave comprising two side bands and an unmodulated carrier component, a local oscillator, means for combining said received .wave with currents from. said local source to produce a wave of an intermedlate freunmodulated component, means for combining said local carrier oscillations with said unsuppressed side band to produce a signal of a third frequency, and means for indicating said last mentioned signal.

4. In a radio signaling system, means for receiving a wave comprising two modulated components and an unmodulated component, a local oscillator, means for combinin said received wave with a wave from said local oscillator to produce an intermediate frequency wave, means for amplifying said intermediate frequency wave, a filter adapted to suppress one of the modulated components and the unmodulated component of said intermediate frequency wave, a second filter ada )ted to pass both modulated components tiereof, a local oscillator adapted to supply locally oscillations of the frequency of the suppressed unmodulated component, means for combining said modulated component with said local oscillations to produce a signal of a third frequency, means for indicating said last mentioned signal,

and switching means whereby either one or the other of said above mentioned filters is connected between said amplifying means and said last mentioned combining means, said switch being adapted to deenergize said second mentioned source of local oscillations when said second mentioned filter is connected in circuit and to energize said source when said first mentioned filter is connected.

5. A radio receiving circuit comprising means for receiving a wave comprising modulated and unmodulated components, a local oscillator, means for'comfbining said received wave with currents from said local oscillator whereby a wave of intermediate frequency is produced, said combining means being adapted to suppress other signals of said intermediate frequency produced by the interaction of two received waves, means for amplifying said intermediate frequency wave; a filter adapted to pass said modulated and unmodulated components thereof, a second filter adapted to pass one of said modulated components only and to suppress the other of said modulated components and the unmodulated component, switching means for connecting either one or the other of said filters in circuit, means for rectifying said intermediate frequency signal comprising two space discharge detectors in push-pull relationship, a source of local oscillations for supplying a local carrier to said push-pull detector when said second mentioned filter is connected in the circuit, means for rendering inoperative one of said space discharge detectors when said first mentioned filter is connected in circuit, and means for determining said received signal. 0

6. A radio receiving system comprising a loop antenna adapted to. receive a transmitted wave composed of unmodulated and modulated components, a source of local os-.

cillations, a detector comprisin space discharge devices connected in pusdi-pull relationship for combining said local oscillations with said received wave to produce a Wave of an intermediate frequency, said detector being adapted to suppress signals of said intermediate frequency produced by the combinatlon of two received waves, a space discharge amplifier for amplifying said intermediate frequency wave, a filter adapted to pass the unmodulat ed and modulated components of said intermediate frequency wave, a second filter adapted to pass one of said modulated components only and to sup-,

switch for deenergizing said last mentioned source when said first mentioned filter is connected in circuit and for energizing said source when said last mentioned filter is connected in. circuit, means comprising said switch for rendering inoperative one of said space discharge devices comprising said'second mentioned detector when said. first mentioned filter is connected in circuit, and means for 'mdlcatmg said -rece1ved signal. 7. A radio recelvlng antenna-capable of,

radiating oscillations supplied thereto, a;

push-pull vacuum tube detector having its input circuit connected thereto, a local source of oscillations connected to the input circuit of said detector, said connection lying in the common path of the push-pull detector input circuit and said antenna being oppositely connected'tothe grid circuits of the individual vacuum tubes, whereby radiation of the locally produced oscillations from said antenna is revented.

In witness w ereof, we hereunto subscribe our names this 30th day of J uly,'A. D., 1925.

JOHN C. GABRIEL.

GEORGE M. THUR-STON. 

